The present invention relates to a document handling system and more particularly relates to an apparatus that automatically registers documents in a tray against a rear and a side registration surface of the tray. This apparatus is particularly suited for a recirculatory document (precollation copying) system in which documents are fed from the bottom of a stack.
It has become desirable to provide for automatic and accurate feeding and registration of individual original document sheets being copied, in order to utilize the higher speed copying capabilities of new copiers. However, one of the most important, and difficult to achieve, requirements for automatic handling is the accurate and reliable, but safe, registration of the original document at the proper position for copying. Conventionally, the document is desirably automatically either center registered or corner registered (depending on the copier) by the document handler at a pre-set registration position relative to the copier platen, with two orthogonal edges of the document aligned with two registration lines of the copier platen, i.e. with the original document aligned with the copier optics and copy sheet registration system. This registration accuracy is desirably consistently within less than 1 millimeter. If the document is not properly registered, then undesirable dark borders and/or edge shadow images may appear on the ensueing copy, or information near an edge of the document may be lost, i.e. not copied onto the copy sheets.
Document handling system in the past have been equipped with various document transports to move the original document sheets over the copier platen and into and out of registration. It is known in the art to register the original document for copying at the appropriate position relative to the transparent copying window in various ways. Typically, the document sheet is registered by driving it against a gate or stop at one edge of the platen. This may comprise projecting aligned fingers, or roller nips, or a single vertical surface, against which an edge of the sheet is driven into abutment. An important function of such registration is to also de-skew the moving original document, i.e., to properly align it with the registration lines as well as to determine and control its registration position.
However, many such known recirculating document handlers drive a document onto the platen and register only the lead or trail edge of the document, without precisely side (laterally) registering the document. Any side registration of the document that occurs in such systems is performed prior to moving the document onto the platen, and is generally merely that provided by the edge side guides of the document tray, which must be set to accommodate the maximum lateral dimensions of the largest document systems, a system for also side registering or positioning the document after it is on the platen is used, i.e., positioning of the original on two axis with respect to the desired imaging position on the platen.
The use of top restacking and bottom feeding document recirculation aggravates the above-discussed problem of accurate registration of the document being fed. For example, with bottom sheet feeders, since the stack height and weight is variable, the normal force on the bottom sheet, (pressing the stack against the bottom sheet and pressing the bottom sheet against the stack tray) is also variable. Further, even if a document sheet is laterally re-registered as it is being restacked, the agitation of the stack by the bottom feeder, particularly if an air sheet separation system is used, may disturb the initial alignment of the sheet as the sheet works its way down from the top of the stack to the bottom before it is fed out again.
Because of variations in the sizes of documents of even the same standard size, it is often not possible to maintain lateral alignment by edge guides or even with edge joggers or tampers. Those sheets in the stack which are undersized can still vary in position by the difference in size between those smaller sheets and the larger sheets in the stack, since the edge guides and/or conventional side joggers are limited in setting by the widest sheets in the stack. Obviously, if edge guides were to be moved in, i.e., set for the smaller sheets, this would not allow flat stacking or settling or unobstructed feeding out of the larger sheets from between these edge guides. Thus, the side guides may have to be set apart by up to a several millimeters greater width than the width of the narrowest sheet in the stack, allowing a corresponding lateral misregistration of such narrower sheets. [As used herein, width or narrowness refers to the sheet dimension transverse its circulative feeding direction, regardless of whether the sheet is fed edgewise (long edge first) or lengthwise (short edge first). The former is more conventional].
Binding of the sheets between edge guides which are too close together, or even forcibly dragging the sheet against one edge guide, can cause wear or damage to the document edges, particularly for the multiple circulations used in precollation copying. Frictional rubbing of documents against only one edge guide, especially over the platen, can also cause skewing of the document as it is being fed. An edge guide on the platen itself has other disadvantages, e.g. potential "show around" printout of a line or shadow on the sides of the copy sheets, or loss of an edge image. Thus, platen edge guides are not generally used, or are withdrawn, in an automatic document feeder. Constant edge tampering or jogging is even worse, because it typically requires repeatedly forceably striking the edges of the stack, usually in only a small and constant area thereof, which can deform or otherwise damage these document edge areas, particularly over the extended time of repeated document recirculations. Older, and/or more brittle documents and extending oversize documents in a set are particularly vulnerable to this damage. In any case, as noted, such edge jogging cannot positively register all of the undersized documents in a set.
In contrast, with the disclosed system herein, each bottom sheet in the stack is individually, and gently, aligned directly against a defined reference lateral edge guide regardless of variations in size of the sheets in the stack, i.e. for a wide range of sheet widths, and without any interference of feeding or larger sheets. The sheets are not aligned by hitting their edges. Rather, they are allowed to fall due to gravity against an inclined registration edge. By using a recirculating document handler (RDH) which minimizes document sheet skewing in the feeding system from the document set stack to the registration position on the platen no other lateral registration system is needed for the entire RDH system. Thus, there is no significant edge guide drag on the documents.
Further details of an exemplary recirculating document handler with which the present invention may be utilized, including relevant teachings of such features as disclosed in FIG. 1 herein, are disclosed in U.S. Pat. No. 4,418,905 which is incorporated herein by reference to the extent necessary to practice the present invention.
A preferred specific feature of the present invention is to provide a recirculating document handling apparatus that includes the combination of less rear corner restriction and straight ramp tray configuration that automatically registers documents against a rear registration surface, especially during restack, bends documents in only one direction during feeder acquisition, and feeds documents in a straight line. In combination, this system eliminates side registration over the platen and side stack jogging during restack of documents.
Further features and advantages of the invention will be better understood by reference to the following description, and to the drawings forming a part thereof.